Full-Endoscopic Lumbar Discectomy vs Standard Discectomy: A Noninferiority Study on Clinically Relevant Changes
===============================================================================================================

* Joel Beck
* Olof Westin
* Mikael Klingenstierna
* Adad Baranto

## Abstract

**Background** Surgery for lumbar disc herniation (LDH) has had a remarkable technological development during the past 20 years. Microscopic discectomy has traditionally been the gold standard method to treat symptomatic LDH before the introduction of full-endoscopic lumbar discectomy (FELD). The FELD procedure allows unsurpassed magnification and visualization and is currently the most minimally invasive surgical technique. In this study, FELD was compared with standard surgery for LDH, with a focus on medically relevant changes in patient-reported outcome measures (PROMs).

**Purpose** The purpose of this study was to investigate whether FELD is noninferior to other surgical methods for LDH surgery in the most common PROMs, including postoperative leg pain and disability, while still reaching the necessary thresholds for relevant clinical and medical improvements.

**Methods** Patients undergoing a FELD procedure at the Sahlgrenska University Hospital, Gothenburg, Sweden, between 2013 to 2018 were included. A total of 80 (41 men and 39 women) patients were enrolled. The FELD patients were matched 1:5 to controls from the Swedish spine register (Swespine) who had a standard microscopic or mini-open discectomy surgery. PROMs, including the Oswestry Disability Index (ODI) and the Numerical Rating Scale (NRS), as well as the patient acceptable symptom states (PASS) and the minimal important change (MIC), were used to compare the efficacy of the 2 surgical approaches.

**Results** The FELD group achieved medically relevant and significant improvements noninferior to standard surgery within the predefined thresholds of MIC and PASS. No differences could be found in disability measured by ODI FELD −28.4 (SD 19.2) vs standard surgery −28.7 (SD 18.9) or leg pain NRSLeg FELD −4.35 (SD 2.93) vs standard surgery −4.99 (SD 3.12). All intragroup score changes were significant.

**Conclusions** The FELD results are not inferior to standard surgery 1 year postoperatively after LDH surgery. There were no medically significant differences regarding MIC achieved or final PASS in any of the measured PROMs, including leg pain, back pain, or disability (ODI) between the surgical methods.

**Clinical Relevance** The present study highlights that FELD is noninferior to standard surgery in clinically relevant PROMs.

**Level of Evidence** 2.

*   Lumbar disc herniation
*   full-endoscopic lumbar discectomy
*   minimal invasive spine surgery
*   FELD
*   PROMs

## Introduction

Historically, lumbar disc herniation (LDH) surgery was an extensive procedure with significant morbidity.1 With the introduction of full-endoscopic lumbar discectomy (FELD), a truly minimally invasive surgical technique has been developed.2,3 Current research has yet to show that a FELD procedure has significant medical gains and advantages.4 However, if proven noninferior to other methods, one can hypothesize that the potential for minimal tissue damage and decreased surgical and hospital length of stay might motivate the initial investment in equipment and training.5 

## Materials and Methods

The hypothesis of the study was that patient-reported outcome measures (PROMs) in a FELD cohort matched to LDH patients having standard surgery were noninferior in regard to minimal important change (MIC) and postoperative patient acceptable symptom state (PASS) for all measured PROMs.5–7 

### Study Design

This study was conducted as a matched cohort study, comparing FELD patients operated at Sahlgrenska University Hospital, Gothenburg, Sweden between 2013 and 2018 with controls having standard LDH surgery (microscopic or mini-open procedure) from the Swespine register.8 A total of 92 FELD patients were initially enrolled, and 80 patients with complete 1-year postoperative follow-up were analyzed in the study. Patients were matched according to age ±3 years, sex, preoperative leg pain duration, and lumbar level of disc herniation.

### Patient-Reported Outcome Measures

The Oswestry Disability Index (ODI) was used to assess the disability.9 Leg and back pain were rated with the Numerical Rating Scale (NRS 0–10).

At 1-year follow-up, a qualitative single-item leg/back pain question-global assessment (GALeg/Back) was formulated as “How do you rate your leg/back pain today as compared with before you had your back surgery?” with a 6-level response option: 0—had no preoperative leg/back pain, 1—pain free, 2—much better, 3—somewhat better, 4—unchanged, 5—worse.10 

### Minimal Important Change and Patient Acceptable Symptom State

To study clinically important differences, use of the MIC score and PASS have been suggested. The PASS gives a threshold on what a mean tolerable baseline level is for a PROM score (“feeling good”), whereas the MIC value states the minimum change needed to be perceived as meaningful for the patient and still being able to be registered on the PROM scale (“feeling better”). Values used in this study are in-line with and derived from previously published articles and are presented in Table 1.11–19 

View this table:
[Table 1](http://ijssurgery.com//content/17/3/364/T1)

Table 1 
MIC and PASSa values used in the study.

### Surgical Indication and Inclusion Criteria

The indication for a FELD discectomy was unsustainable leg pain for more than 6 weeks, with or without motor and sensory deficit, which failed to respond to conservative or physiotherapeutic treatment.20 Exclusion criteria were cauda equina syndrome, previous spinal surgery, lumbar fracture, and incomplete preoperative data.

### Surgical Techniques

#### Full-Endoscopic Lumbar Discectomy

The surgical FELD method has been described thoroughly in several original articles and was performed according to the description by Rutten et al.20–22 

#### Standard Procedures

The control group had a conventional lumbar discectomy, either by a microscopic or mini-open approach. These techniques can be considered comparable in all relevant long-term outcomes.6,23,24 

### Statistical Analysis

The data from the FELD and control groups were compiled using SAS statistical software version 9.4 (SAS Institute Inc) for statistical analysis. Descriptive statistics for patient demographics and outcomes were reported as proportion and count for categorical variables. Continuous variables were reported as mean and SD and with median and the first and third quartiles. A post hoc power analysis for NRSLeg was performed at 80% with an intergroup noninferiority difference of <2 to verify a sufficient sample size. The Fisher exact test was used for dichotomous variables, the Mantel-Haenszel χ2 test was used for ordered categorical variables, and the Pearson χ2 test was used for nonordered categorical variables. The Wilcoxon test was used for paired data. McNemar test was used to compare paired samples for nominal and dichotomous variables. All significance tests were 2 sided and conducted at the 5% significance level. The multilevel GALeg and GABack were dichotomized to allow for a robust comparison between the groups.

## Results

A total of 80 FELD patients were eligible for the study. They were matched to 400 controls from the Swespine register, creating a 1:5 inclusion ratio. The baseline values for the groups are shown in Table 2. Mean preoperative leg pain intensity measured by NRSLeg for the FELD group was 7.34 SD (1.98), and mean back pain (NRSBack) was 5.11 (SD 2.74). The patients were, according to their mean ODI of 46.5 (SD 18.5), severely affected by their LDH, resulting in significant disability. There were no significant differences between the groups at inclusion.

View this table:
[Table 2](http://ijssurgery.com//content/17/3/364/T2)

Table 2 
Demographic parameters at baseline.

At the 1-year follow-up, the FELD group rated their residual leg pain NRSLeg 2.69 (SD 2.68), and their NRS leg pain change score (ΔNRSleg) showed a –4.35 (SD 2.93) difference (baseline – 1 year follow-up) or a 60.2% (SD 36.7%) decrease in leg pain. A comparison with the control group revealed no differences in any of the recorded PROMs as illustrated in Table 3.

View this table:
[Table 3](http://ijssurgery.com//content/17/3/364/T3)

Table 3 
Postoperative patient-reported outcome measures for FELD and Swespine controls.

In analogy with the postoperative decrease in NRSLeg + Back, for the FELD group, the reported mean residual disability measured by the ODI 17.3 (SD 16.7) was below the PASS without any differences between the groups. Among the FELD patients, 58.2% reached PASS in NRSLeg compared with open surgery (71.7%). The difference was not significant (*P* = 0.055). As illustrated in Table 4 , by using the predefined PASS score for ODI set at 22, the FELD group attained a similar proportion of patients achieving PASS as the control group.

View this table:
[Table 4](http://ijssurgery.com//content/17/3/364/T4)

Table 4 
Attained PASS scores for the groups.

The MIC values are provided in Table 5. In NRSLeg, 60.5% (FELD) and 73.6% (controls), respectively, attained the MIC or better. No significant differences between the groups were recorded for the NRS or ODI.

View this table:
[Table 5](http://ijssurgery.com//content/17/3/364/T5)

Table 5 
MIC values for the different surgical groups.

## Discussion

The main finding in the study is that FELD is noninferior to standard surgery and showed medically relevant improvements in clinically used PROMs, within specified MIC and PASS values. No clinically relevant differences could be discerned regarding leg and back pain–specific outcomes, disability, or quality-of-life scores at 1-year follow-up.

Leg pain (sciatica) and its detrimental effect on quality of life is the most common complaint for LDH. In our study, the entire study population had severe preoperative leg pain (NRSLeg with a mean 7.04 [SD 2.15]) that responded positively to surgery. The FELD group achieved a high level of pain reduction measured in NRSLeg, where 60.5% reached the MIC threshold and 58.2% reached PASS, which were comparable with that of standard surgery. The intergroup differences were not statistically significant, but a very slight benefit could be noted for the standard surgery group in postoperative residual leg pain, perhaps illustrating a potential benefit for the extensive decompressive approach of a standard procedure vs the ultraminimal invasive FELD in certain cases. This is in analogy with a previously published randomized controlled trial that also could not discern medically relevant differences between the surgical methods.25,26 

However, back pain can also be a significant factor in the symptomatology of LDH patients. Moreover, residual back pain is known to be a major patient complaint following LDH surgery.27 Perceived increased back pain after spinal procedures is such an established concept that it has become an entity of its own, with thousands of people suffering from *failed back surgery syndrome* or, more recently and perhaps more adequately named, *chronic pain after spinal surgery*.28 A method to decrease the amount of tissue trauma in LDH surgery could potentially offer huge advantages for patients and doctors alike.

Regarding disability, both the FELD and control group had more than 63% of patients reaching MIC in ODI, whereas only 24.9% did not attain the PASS limit. Both groups had similar changes in ODI, and FELD was noninferior in ODI.

The GALeg and GABack have been suggested to be used as surrogate variables for assessing surgical outcomes, and, in analogy with the other measured PROMs in this study, no intergroup differences were found.

The standard LDH surgery still offers excellent efficacy and value, and FELD should be considered an alternative surgical approach but perhaps still in search of its true signature indication where superiority can be proven. Decreasing the amount of tissue trauma and postoperative back pain is a tantalizing prospect for physicians and patients alike. The increasing prevalence of obesity poses a particular risk for operative and postoperative management and complications, and this might be the perfect indication for FELD, especially for lateral or foraminal disc herniations.

During the past 15 years, FELD has evolved to become a viable alternative to other visualized operative techniques for discectomy.24,29–31 Theoretically, there are several advantages with the method that would facilitate a safer and less invasive surgery with potential for enhanced recovery and superior results. Modern endoscopes offer an incomparable overview, illumination, and visualization of the operative field when compared with either microscopic enhancement or simple loupes, and the decreased amount of intraoperative trauma has the potential to reduce the risk of postoperative persistent back pain.

### Limitations

This study comprised a consecutive cohort from a single center. The study cohorts were matched on gender, age, preoperative pain duration, and level of disc herniation only. While all of these parameters are relevant and important in a preoperative selection process, none of them are very strong predictors for currently used PROMs. A more extensive matching procedure might eliminate some of the inherent bias in this study design.

## Conclusion

The FELD results are not inferior to standard surgery 1 year postoperatively for LDH. There were no significant differences regarding MIC achieved or final PASS in any of the measured PROMs, including leg pain, back pain, or disability (ODI) between the surgical methods. FELD is an alternative to standard surgery for LDHs.

## Footnotes

*    **Funding**  The authors acknowledge the financial support of The Medical Society of Gothenburg, Sweden and grants from the Swedish state under the agreement between the Swedish government and the county councils, the ALF agreement (Adad Baranto, ID number 238801).

*    **Declaration of Conflicting Interests**  Adad Baranto is a clinical lecturer for Riwospine, GMBH, and recieves reimbursement for teaching positions. All other authors report no conflicts of interest in this work.

*    **Ethics Statement**  The present study was approved by the Regional Ethical Review Board in Gothenburg at The Sahlgrenska Academy, Gothenburg University, Gothenburg, Sweden (ID number: 753-17).

*   This manuscript is generously published free of charge by ISASS, the International Society for the Advancement of Spine Surgery. Copyright © 2023 ISASS. To see more or order reprints or permissions, see [http://ijssurgery.com](http://ijssurgery.com).

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